Fire Hopping is done by performing a Drift ending with a speed boost, and immediately hopping left and right while the fire is spewing out the exhaust (hence the name). Doing so will increase the speed and distance of the Drift Boost, as players lose less speed while airborne, and a successful Fire Hop can give you an extended boost.

The hopping is the most difficult part, as you'll need to adjust your jumping so that you avoid crashing into wall, and set yourself up for the next drift. You can Fire Hop up to 4 or 5 times for the duration of the longest draft boost, but even 1 or 2 jumps will increase your speed. Note that if you jump while not boosting, you will actually slow down, so don't over-jump.

Fire Hopping can be done with almost any vehicle (excluding the Sport Bike or its variants due to inside drifting) and works best with high speed vehicles.

Other things to keep in mind:

Using this technique while going downhill could actually slow you down.

Fire Hopping is a great trick to subtract precious seconds from your time in Time Trials, but those seconds mean very little in multi-player. Additionally, this technique requires a significant amount of skill to perfect, like mastering shortcuts and cornering. It's not recommended for use in Grand Prix or Online, as the danger of being hit by items or players could ruin a successful Fire Hop.